Try removing your email account from your phone, restart the phone (turn it off and back on) and then add the account again.
If that doesn't help then you may want to check that there is nothing else on the device that is interfering and causing the error. Try checking the device for any malware, viruses, bad apps, etc.
Also, when you did the reset, if you chose the option to keep your personal stuff, then this would not have removed any problems. Should you still get this after checking the device for other things, you may want to then save/backup your personal stuff (photos, contacts, etc. -not apps as you can't back those up) and do a "Hard Reset" of the device. This will wipe everything and then reinstall the original OS and...